The present invention relates to a titanium dioxide photocatalyst structure that has excellent photocatalytic actions and light transmissivity (or transmittance) and enables members of various substances, which require transparency particularly, to have photocatalytic actions. The present invention further relates to a lighting device and a window glass which employ such a titanium dioxide photocatalyst structure.
Heretofore, there have been known photocatalysts that exhibit activities, by which the decomposition and oxidation of substances are accelerated, when irradiated with light. Recently, attempts or the like have been made to remove air pollutants such as sulfur oxides and nitrogen oxides by utilizing the photocatalysts. Moreover, attempts have been further made to use titanium dioxides as the photocatalysts (see, for example, Japanese Patent Laid-Open Nos. 6-385/1994, 6-49677/1994 and 6-39285/1994 Official Gazettes).
By the way, in recent years, there has been a growing interest in globally environmental pollution. Meanwhile, the demand for removing substances such as CO2, NOX and SOX has grown. Moreover, a plan for creating amenity space by eliminating toxic substances has been devised. Thus, the demands for deodorizing living space and for making the living space antibacterial, soil-resistant and mildew-proof have grown increasingly.
It is accordingly conceived that the aforementioned titanium dioxide photocatalyst is utilized for removing such pollutants. However, in the case of the conventional titanium dioxide photocatalysts, generally, gaseous or liquid materials to be treated are introduced into a container accommodating the photocatalyst and are thus made to be in contact with the photocatalyst, and simultaneously, light is introduced from the exterior thereto and is applied onto the photocatalyst.
Further, in such a case, for the purpose of increasing the contact area between the material to be treated and the photocatalyst and efficiently applying the light onto the photocatalyst, attempts or the like have been made to produce the photocatalyst in minute-particle form or to hold the photocatalyst on a transparent base material.
However, in the case of the aforementioned conventional titanium dioxide photocatalyst, although the contact area between the photocatalyst and the material to be treated can be increased by, for instance, producing the photocatalyst in minute-particle form, the effective area of the photocatalyst, by which light is received, cannot be increased very much. Consequently, it is difficult to largely enhance the total catalysis effects thereof
Further, in the case where the titanium dioxide photocatalyst is formed in film form on, for example, a glass substrate or the like, the titanium dioxide photocatalyst itself has low transparency. This is because it has been heretofore considered that methods suitable for forming a photocatalyst in film form to thereby obtain practical photocatalysis are limited to a method of forming a titanium dioxide sol on the substrate by sintering and a method of producing titanium dioxide in fine powder form, dissolving the powder by using a binder and then applying the dissolved powder onto the substrate. However, in the case of employing the former method, a photocatalyst, which has high activity and a certain measure of transparency, can be obtained, though it is necessary for obtaining the film, whose strength is sufficient for practical use, to set a sintering temperature at a value which is not lower than the softening temperature of glass. Thus, at least, it is impossible to form the photocatalyst on the glass substrate. Besides, regarding the light transmissivity, this photocatalyst tends to become clouded. It is difficult for this photocatalyst to transmit visible light to such an extent that the transparency can be obtained. In this sense, this photocatalyst is close to opaque. In contrast, in the case of the latter method, although the step of sintering is unnecessary, the photocatalyst becomes clouded and opaque because fine titanium dioxide powder is applied to the substrate.
Further, in the case of titanium dioxide produced in film form by performing a sol-gel method and CVD method which have been well known in the field of such a kind heretofore, the transparency can be ensured, whereas the activity of the catalyst, which has a practical level, is not obtained.
Thus, all of the conventional titanium dioxide photocatalysts, which exhibit the photocatalytic activities of practical levels, are substantially opaque. Therefore, even in the case that this conventional photocatalyst is formed on, for example, the front surface of a transparent glass substrate or the like, light applied from the back surface of the glass substrate cannot effectively reach the front surface portion of the photocatalyst. Consequently, only light applied from the front surface portion, on which the photocatalyst is formed, of the substrate can be utilized. Hence, in the case that the cleaning of indoor air is performed by forming this photocatalyst on, for instance, the surface of a window pane, it naturally follows that the photocatalyst is formed on the surface of the glass, which faces the inside of a room. Thus, only light applied from the inside of the room that can be utilized for obtaining the photocatalytic activity. Consequently, there has been a serious defect that sunlight cannot be utilized therefor.
Thus, in the case of the conventional titanium dioxide photocatalyst, titanium dioxide, which performs the photocatalysts, itself is substantially opaque. Consequently, there occurs a limit to the enhancement of the photocatalytic activity. Moreover, the range of application of the photocatalyst is extremely limited.
Furthermore, there has been made an attempt to apply powdered photocatalyst to the outer surface of a discharge lamp to thereby impart a deodorization function thereto (see Japanese Patent Laid-Open No.1-169866 Official Gazette). Additionally, there has been made another attempt to cover the periphery of an illuminating lamp with a net constituted by a glass filter, which is coated with a photocatalyst (see Japanese Patent Laid-Open No.1-139139 Official Gazette), thereby performing a deodorization by utilizing a photocatalytic action at a place where illuminance is high, namely, at a place closer to the illuminating lamp. Besides, there has been made still another attempt to decompose ambient offensive odor (or malodor) substances by depositing a titanium dioxide film on the surfaces of spectacle lenses according to a sputtering method (see Japanese Patent Laid-Open No.2-223909 Official Gazette).
However, the discharge lamp described in the aforementioned Japanese Patent Laid-Open No.1-169866 Official Gazette is configured only by applying anatase-type titanium dioxide powder, whose grain diameter is 500 xc3x85, onto the outer surface of a discharge container. Thus, this discharge lamp is inferior to other lamps in light transmissivity and abrasion resistance. It is obvious that, even if the applied titanium dioxide is baked, a high temperature is needed and there are obtained only discharge lamps which are inferior to other lamps in light transmissivity. Therefore, in the case of this discharge lamp, the photocatalyst has little effect. Further, this discharge lamp is in a state in which the powder adheres to the surface thereof and the degree of the unevenness of the surface thereof is high. With such a structure, this discharge lamp is easily stained and is liable to gather dusts.
Moreover, regarding the air-cleaning spectacle described in the Japanese Patent Laid-Open No. 2-223909 Official Gazette, although the titanium dioxide films are formed on the surfaces of the spectacle lenses by a physical method such as an ion plating method, the objective device configuration and data concerning the identification of titanium dioxide, the crystalline structure of the (thin) films and the judgement on the deodorization effects are not sufficiently disclosed in this official gazette.
Furthermore, in the case that the films are formed by the physical method such as a sputtering method, a considerably long film formation time is required to obtain a film thickness by which practical photocatalytic actions can be caused. This causes problems in respect of the productivity and the stability of the quality of films. Consequently, such physical film formation processes have drawbacks in that such processes are difficult to be used as manufacturing processes of general-purpose industrial products.
Further, the conventional illuminating lamp coated with a titanium dioxide film (or layer) has defects in that the light transmissivity is low because the powdered titanium dioxide film is used and thus this film is substantially opaque, in that it is difficult for light, which is emitted from the inside of the illuminating lamp, to reach the outermost surface of the titanium dioxide layer, to which contaminants in the air most easily adhere, in that therefore, the quantity of available light is considerably smaller than the quantity of available light in the case of depositing a transparent titanium dioxide film on the lamp, in that thus, the amount of decomposed contaminants is very smaller in comparison with the amount thereof in the latter case, and in that the surface of the lamp is easily stained owing to the unevenness of the surface thereof.
Incidentally, in the case of the discharge lamp and the spectacle, which are respectively described in the aforementioned Japanese Patent Laid-Open Nos. 1-169866 and 2-223909 Official Gazettes, objects to be decomposed are mainly offensive odor substances. Namely, primary objects or purposes of these discharge lamp and spectacle are not the decomposition of fat and oil.
The present invention is accomplished against the aforementioned background. The present invention aims at providing a titanium dioxide photocatalyst structure that has excellent photocatalytic actions and light transmissivity and enables members of various substances, which require transparency particularly, to have photocatalytic actions and further aims at providing a method for producing such a photocatalyst structure.
To solve the aforesaid problem, in accordance with the present invention, there is provided a titanium dioxide photocatalyst structure which comprises:
a transparent glass substrate having first and second opposing surfaces, the first surface of the aforesaid substrate receiving light from an external light source; and
a titanium dioxide film having first and second opposing surfaces, a light transmittance of the aforesaid titanium dioxide film being at least 50% for light having a wavelength of 550 nm, the first surface of the aforesaid titanium dioxide film being formed on the second surface of the aforesaid substrate, whereby light transmitted from the aforesaid external source through the first and second opposing surface of the aforesaid substrate and through the first surface of the aforesaid titanium dioxide film to t he second surface thereof causes photocatalytic action to be generated on the second surface of the aforesaid titanium dioxide filming.
Further, in accordance with another aspect of the present invention, there is provided an illuminating device having a light emitting portion, provided in a glass container, for radiating light, which includes visible light as a main component and further includes an ultraviolet component, which comprises: a titanium dioxide film which is formed on a surface of the aforesaid glass container having first and second opposing surfaces and is adapted to have a photocatalytic activity due to absorption of ultraviolet light and to transmit at least 50% of visible light, whose center wavelength is 550 nm, radiated from the aforesaid light emitting portion and having passed through the aforesaid glass.
Moreover, in accordance with another aspect of the present invention, there is provided a window glass provided with a titanium dioxide film, formed on at least one of sides of a glass sheet or plate, wherein the aforesaid titanium dioxide film is adapted to have a linear transmittance of 50% or more when measured by using light having a wavelength of 550 nm and to have a linear transmittance of 50% or less when measured by using light having a wavelength of 350 nm, and wherein the aforesaid titanium dioxide film has ability to decompose 0.5 xcexcg of linoleic (or linolic) acid per square centimeter of the film for one hour in a case that the film is irradiated with ultraviolet light including light, whose wavelength ranges from 300 to 400 nm, and having a power density of 5 mW/cm2.
Thus, a titanium dioxide film, which has at least photocatalytic activity and light transmittance corresponding to light having a wavelength of 550 nm is not less than 50% , is formed on a transparent substrate. Thereby, the titanium dioxide photocatalyst structure can have excellent photocatalytic action and optical transmissivity. Moreover, the titanium dioxide photocatalyst structures can be used as members composing various structures such as a glass window, which are especially required to have light transmissivity.
This is owing to the fact that as a result of setting the titanium dioxide film in such a manner that the light transmittance corresponding to light having the wavelength of 550 nm is not less than 50%, the substantially increasing of light irradiation efficiency required to obtain photocatalytic activities can be easily achieved and simultaneously, the transparency corresponding to visible light can be ensured. Namely, if setting the titanium dioxide film in such a manner that the light transmittance corresponding to light having the wavelength of 550 nm is not less than 50%, the titanium dioxide film inevitably has the transmissivity corresponding to light, which gives the photocatalytic activity (and which has the wavelength of about 400 nm), in such a way that the degree of the transmissivity is sufficient to effectively utilize light applied thereto from the front and back thereof. Therefore, when both of the front and back surfaces of this titanium dioxide photocatalyst structure are irradiated with different light, respectively, the light rays respectively coming from both of the surfaces thereof reach the surface portion, which is in contact with the exterior, of the titanium dioxide film in such a manner as to be added to each other. Namely, the efficiency in applying light onto the surface portion of the titanium dioxide film can be substantially increased. Thereby, the photocatalytic activity of the surface portion of the titanium dioxide film can be substantially increased in response to this, so that excellent photocatalytic activity can be obtained. Simultaneously, as a consequence of setting the titanium dioxide film in such a manner that the light transmittance corresponding to light having the wavelength of 550 nm is not less than 50%, the sufficient transparency corresponding to visible light can be secured inevitably. Consequently, this titanium dioxide photocatalyst structure can be used as a member of various structures especially required to have the transparency, for example, a glass window, an illuminating system, a mirror and a glass door. The present invention can have distinguished advantages in that actions of eliminating carbon dioxide and air pollutants (for example, NOX and SOx) from indoor space, of deodorizing the indoor space and of making the indoor space antibacterial, soil-resistant and mildew-proof are achieved by the window pane itself without using special equipment. Additionally, the present invention can obtain eminent merits in that in the case of cleaning the room by applying the photocatalyst structure to the window pane, sunlight can be extremely utilized. Moreover, especially, in the case of applying the photocatalyst structure of the present invention to a building or the like, in which glass materials are highly used, of the type that has become common in recent years, the photocatalyst structure of the present invention has immeasurable advantages in cleaning the living space. In addition, the photocatalyst structure of the present invention can be applied to a glass door or the like of a shelf, which includes the door or the like, for storing, for instance, precision devices such as a camera which should be kept away from molds and corrosion. Thus, the range of application of the photocatalyst structure of the present invention is extremely wide. Further, a titanium dioxide film having sufficient photocatalytic activity and simultaneously having the light transmittance, which is not less than 50% correspondingly to light having a wavelength of 550 nm, can be obtained by setting the thickness of the titanium dioxide film at a value of 0.1 to 5 xcexcm. In the case that the thickness of the photocatalyst structure is less than 0.1 xcexcm, sufficient photocatalytic activity cannot be obtained. In contrast, in the case that the thickness of the photocatalyst structure exceeds 5 xcexcm, the light transmittance corresponding to the light having the wavelength of 550 nm is less than 50% . Consequently, sufficient transparency cannot be obtained.
Moreover, the titanium dioxide film contains anatase crystals. Thereby, the photocatalyst structure further excels in photocatalytic activity.
Furthermore, a precoat film having transparency is disposed between the transparent substrate and the titanium dioxide film. Thus, the material of the transparent substrate penetrates into the titanium dioxide film, so that the photocatalytic activity of the titanium film can be prevented from being degraded. Moreover, the range of materials of the transparent substrate to choose can be extended. Furthermore, in the case of forming a titanium dioxide film directly on the transparent substrate, the titanium dioxide film should have a thickness sufficient to the extent that even when the material of the transparent substrate penetrates into the titanium dioxide film, the material cannot reach titanium dioxide on which charge separation action should be exerted. The present invention, however, eliminates the necessity of making the film thick to such an extent. Thus, even when the titanium dioxide film is made to be extremely thin regardless of what kind of materials the substrate employs, the photocatalytic activity can be sufficiently enhanced. This is very significant from the view point of essential enhancement of efficiency in irradiating light, and of improvement of transparency.
In the case that the thickness of the precoat film is 0.02 to 0.2 xcexcm, even when taking materials, which can be employed as those of the precoat film, into consideration, the photocatalyst structure of the present invention can obtain advantages in that sufficient transparency can be ensured and that the penetration of the material of the substrate can be blocked. Conversely, in the case that the thickness of the precoat film is less than 0.02 xcexcm, it is difficult to have a sufficient effect on the blockage of the penetration of the material. Further, even in the case that the film, whose thickness exceeds 0.2 xcexcm, is formed, the photocatalyst structure cannot have further advantageous effects on the blockage of the penetration of the material. Moreover, an operation of forming the film becomes complicated. Furthermore, if the film is made of some material, the sufficient transparency cannot be ensured.
In the case that glass is used as the transparent substrate, the extremely wide range of application of the photocatalyst structure of the present invention can be achieved, as previously described. In this case, if the precoat film is made of SiO2, the best transparency and the highest effects on the blockage of penetration of the materials of the substance can be secured.
In a glass container, a titanium dioxide film, which has photocatalytic activity due to ultraviolet light absorption and is, on the other hand, adapted to transmit a light component that is radiated from the aforementioned light emitting portion and is then transmitted by the aforesaid glass container, with the intention of irradiating the photocatalyst, is formed on the surface of the glass container. Thickness of this titanium dioxide film is set in such a manner as not to be less than a value, which is necessary for having photocatalytic activity whose degree is equal to or higher than that of photocatalytic activity required to decompose and remove fat and oil ingredients deposited on the surface of this film in an ordinary life space, and in such a manner as not to be more than a value at which the aforementioned light component, whose magnitude is equal to or more than a magnitude necessary for attaining the object of irradiating the photocatalyst, is transmitted by the film. Thus, there can be obtained an illuminating lamp that has a self-cleaning function in addition to securing the illuminating function.
Moreover, a titanium dioxide film, which has photocatalytic activity due to ultraviolet light absorption and is, on the other hand, adapted to transmit 50% or more of visible light that is radiated from the aforementioned light emitting portion and is then transmitted by the aforesaid glass container and has wavelengths in a range whose center wavelength is 550 nm, is formed on the surface of the glass container. Thus, there is obtained an illuminating lamp that has an extremely excellent self-cleaning function of efficiently decomposing fat and oil gradients typified by oil stains and tobacco tars, which are deposited on the surface thereof, by light emitted from the illuminating lamp itself. This titanium dioxide film of the present invention, which is excellent in the photocatalytic actions, has not only the fat-and-oil decomposing function but has an antibacterial function and a deodorization function. Thus, for example, lamp blacks and tobacco tars deposited on the surface of an interior lamp are relatively easily decomposed by light emitted by the illuminating lamp such as a fluorescent lamp itself. It is, thus, easily conjectured that, as a result, this illuminating lamp is dust-proof and dirt-resistant and excels in an anti-fouling function. Furthermore, this illuminating lamp further has an advantage in that minute quantities of malodorous substances contained in an interior space or unwanted bacteria floating in an accommodation space are easily decomposed or annihilated when adhering to the surface of the glass container or tube of the illuminating lamp. Therefore, this illuminating lamp can be put to various uses such as illumination of: facilities which are required to be kept clean and to accommodate many people gathering therein, especially, hospitals, clinics, medical offices, old-age homes, long-term sanatoria, hotels, offices and food factories; the inside of transportation means such as a train and a bus; and of tunnels and roads.
Incidentally, the provision of the titanium dioxide film on the surface of a glass container has other advantages in that sufficient photocatalytic actions are obtained by utilizing relatively intense light irradiated on the surface of the glass container, and that radiation of harmful ultraviolet light to the exterior is prevented by being almost completely absorbed and being thus cut off by this titanium dioxide film on the surface of the glass container. Further, hitherto, in the case of a fluorescent lamp, it is usual that an ultraviolet absorbent is added to a phosphor (or fluorescent substance) to be applied onto the glass container. The provision of the titanium dioxide film can eliminate the necessity of such a step. In this case, the magnitude of ultraviolet light reaching the titanium dioxide film provided on the outer surface of the fluorescent lamp container is further increased, so that the function of splitting fats and oils is further enhanced.
Furthermore, in the case of a halogen lamp, the fat-and-oil splitting activity is very high. Thus, the halogen lamp is suited to use at places in an ordinary environment in which the lamp is used, especially in an environment where the lamp is very liable to be stained, for instance, in the vicinity of a kitchen.
Incidentally, the amount of fats and oils generated in a daily life space is 0.1 mg per dayxc2x7cm2 (namely, about 4 xcexcg/Hrxc2x7cm2) even at a place to which extremely large amounts of fats and oils would be expected to adhere, for example, in the proximity of a ventilating fan provided at an upper part of a kitchen range in an ordinary home, as described in xe2x80x9cElectrochemistry and Industrial Physical Chemistryxe2x80x9d, 1995, Vol.163, No. 1, p. 11. Moreover, it has been reported that a quantity of a contaminant such as tobacco nicotine and tar is not more than 0.1 mg per dayxc2x7cm2 (namely, about 4 xcexcg/Hrxc2x7cm2) at a living room of an ordinary home. Thus, in the case of considering the ordinary living space, 0.5 xcexcg per dayxc2x7cm2 is an adequate value of the expected amount of the deposited fat and oil. Furthermore, this halogen lamp further has an advantage in that minute quantities of malodorous substances contained in an interior space or unwanted bacteria floating in the interior space are easily decomposed or annihilated when adhering to the surface of the glass container or tube of the illuminating lamp of the present invention having the self-cleaning function.
Further, a titanium dioxide film formed on the surface of the glass container is adapted in such a manner as to reduce ultraviolet light, which passes through the film and has a wavelength of a range whose center wavelength is 365 nm, by 50 to 80% and to decompose or split 1 xcexcg or more of a linoleic acid, which is deposited on the surface of titanium dioxide film, per Hrxc2x7cm2 thereof in a state in which the aforementioned light emitting portion emits light. Thereby, fats and oils deposited on the surface of the film can be decomposed. Moreover, ultraviolet light required to sterilize can be emitted to the exterior. In this case, the fat-and-oil splitting activity of this film is extremely high. Thus, the illuminating lamp can be adapted so that, even when used in the vicinity of the kitchen, the lamp is difficult to contaminate. This lamp is suitable for preventing contamination thereof by the deposited fat and oil in kitchens, in which foods are treated, of a food factory, a food restaurant, a caterer and a stuff canteen.
Film having sufficient photocatalytic activity and transmitting 50% or more of visible light, which has wavelengths of a range whose center wavelength is 550 nm, can be securely obtained by setting the film thickness of the titanium dioxide film at a value in a range of wavelengths from 0.1 to 5 xcexcm. If the film thickness is set at a value which is less than 0.1 xcexcm, the film sometimes cannot obtain sufficient photocatalytic activity. In contrast, if the film thickness is set at a value which exceeds 5 xcexcm, the film sometimes cannot transmit 50% or more of visible light, which has wavelengths of a range whose center wavelength is 550 nm. In addition, the strength and abrasion resistance of the titanium dioxide film is inferior to other lamps. Moreover, the photocatalytic activity of the titanium dioxide can be further enhanced by making the film include an anatase crystal.
Further, the diffusion coating (or cementation) of a part of the ingredient of the glass container is performed by providing a precoat film between the glass container of the illuminating lamp and the titanium dioxide film. Thus, an occurrence of harmful effects such as a reduction in photocatalytic action of the titanium dioxide film can be prevented. Moreover, some latitude in choosing materials of the glass container can be enhanced. Consequently, inexpensive soda lime glass or the like can be used. Moreover, in the conventional case, when deposited directly on the glass container, it is necessary to increase the film thickness of the titanium dioxide film to the extent that, even if the material of the glass container diffuses or penetrates into the titanium dioxide film, the material thereof does not reach the titanium dioxide which performs a charge separation. However, the present invention eliminates the necessity of increasing the film thickness to such an extent. As a result, sufficient photocatalytic actions can be obtained even if the film thickness is considerably reduced, regardless of the material of the glass container.
Furthermore, if the film thickness of the precoat film is 0.02 to 1 xcexcm, even in the case of taking materials which can be generally employed as the material of a precoat film into consideration, such film has an advantageous effect of preventing the penetration of an inhibitor, which comes from the glass container of the illuminating lamp in addition to an advantageous effect of securing the sufficient light transmittance. Conversely, if the film thickness of the precoat film is less than 0.02 xcexcm, the effects of sufficiently preventing the penetration of an inhibitor cannot be obtained. Further, if forming a film having a thickness of more than 1.0 xcexcm, there are no additional advantages that favor the effects of preventing the penetration. Moreover, the film deposition or formation operation becomes complex. Further, in the case of some materials, the light transmittance cannot be secured.
Usually, the best light transmittance and the effects of preventing the penetration of inhibitors is achieved by configuring the precoat film in the glass container by using a material, whose principal ingredient is SiO2, as the material thereof.
At least one layer of the aforementioned precoat film is made to contain a film formed from a material made mainly of indium oxide and/or tin oxide. Thus, the illuminating lamp can have the advantageous effects of preventing a material from penetrating from the glass container of the illuminating lamp whose substrate is similar to that of SiO2 film. In addition, the illuminating lamp can impart an electromagnetic wave shielding function to the glass container of this illuminating lamp owing to the conductivity originated from the indium oxide and/or the tin oxide. The present invention can prevent static electricity, which is generated when turning on the illuminating lamp, and can preventing harmful electromagnetic wave from being radiated into the space. Consequently, this lamp has merits in preventing dusts in a room from adhering thereto, and in reducing noise which exerts ill effects on electronic equipment provided in the room.
Furthermore, there is configured a window glass by comprising a titanium dioxide film, formed on at least one of sides of a glass sheet or plate, wherein the aforesaid titanium dioxide film is adapted to have a linear transmittance of 50% or more when measured by using light having a wavelength of 550 nm and to have a linear transmittance of 50% or less when measured by using light having a wavelength of 350 nm, and wherein the aforesaid titanium dioxide film has ability to decompose 0.5 xcexcg of linoleic (or linolic) acid per square centimeter of the film for one hour in a case that the film is irradiated with ultraviolet light including at least light, whose wavelength ranges 300 to 400 nm, and having a power density of 5 mW/cm2. This enables the window glass to obtain epoch-making self-cleaning performance or function by which fats and oils are effectively split or decomposed by simultaneously securing light transmittance which is sufficient for acting as a window glass. Meanwhile, when conventional window glasses are used in, for instance, a building, or transportation vehicles such as an automobile and a train, soot and tobacco tars adhere thereto. Elimination of such soot and tars is very difficult. However, in the case of the window glass of the present invention, the tobacco tars are relatively easily decomposed and eliminated by utilizing external light and indoor light simultaneously with the adhesion of the soot and tars thereto. Thus, the epoch-making window glass of the present invention can automatically maintain a predetermined clean state at all times without troubles. Needless to say, because the window glass has the ability to split or decompose fats and oils, the decomposition of which is considered in general as being very difficult, the window glass of the present invention has an antibacterial function and a deodorization function.
Titanium dioxide film, which has sufficient photocatalytic actions and linear transmittance of 50% or more corresponding to the wavelength of 550 nm, is obtained by setting the film thickness of the titanium dioxide film at 0.1 to 5 xcexcm. In this case, if the film thickness is set at a value which is less than 0.1 xcexcm, sufficient photocatalytic action is not obtained. Further, if the film thickness exceeds 5 xcexcm, linear transmittance corresponding to the light having a wavelength of 500 nm is less than 50%. Thus, sufficient transparency cannot be secured.
Further, the photocatalyst activity is further enhanced by making the film contain anatase crystals. Enhancement of the photocatalytic activities, especially, the deodorization and the antibacterial activities can be achieved by adding 0.05 to 5 atom % of one element selected from a group of silver, copper and zinc to a titanium atom in the titanium dioxide film. These additives may be added thereto by various addition methods. However, in this case, a photoreduction method utilizing a photocatalytic action is easiest to perform and is most excellent. Thus, for example, in the case of adding silver, this method has an advantage in that high antibacterial activities are maintained not only when the film is irradiated with light, but also when the film is not irradiated. Further, in the case of adding zinc, the adsorption of an acidic substance to the surface thereof can be facilitated by lowering the solid acidity of titanium dioxide. Thus, this is advantageous in the decomposition and elimination.
Occurrences of evil effects, such as the degradation in photocatalytic actions, which is caused as a result of diffusion coating of a part of ingredients of a glass body into the titanium dioxide titanium film, can be prevented by providing a precoat film between the glass body and the titanium dioxide film. Further, some latitude in selecting the material of the glass body can be enhanced. Moreover, in the conventional case, when deposited directly on the glass container, it is necessary to increase the film thickness of the titanium dioxide film to the extent that, even if the material of the glass body diffuses or penetrates into the titanium dioxide film, the material thereof does not reach the titanium dioxide which performs a charge separation. However, the present invention eliminates the necessity of increasing the film thickness to such an extent. Thus, sufficient photocatalytic actions can be obtained even if the film thickness is considerably reduced, regardless of the material of the glass body.
Furthermore, if the film thickness of the precoat film is 0.02 to 1 xcexcm, even in the case of taking materials which can be generally employed as the material of a precoat film into consideration, such film has an advantageous effect of preventing the penetration of an inhibitor, which comes from the glass container of the illuminating lamp in addition to an advantageous effect of securing the sufficient light transmittance. Conversely, if the film thickness of the precoat film is less than 0.02 xcexcm, the effects of sufficiently preventing penetration of an inhibitor cannot be obtained. Further, if forming a film having a thickness of more than 1.0 xcexcm there are no additional advantages that favor the effects of preventing penetration. Moreover, the film deposition or formation operation becomes complex. Further, in the case of some materials, the light transmittance cannot be secured.
Usually, the best light transmittance and the effects of preventing the penetration of inhibitors is achieved by configuring the precoat film in the glass container by using a material, whose principal ingredient is SiO2, as the material thereof. Thus, the illuminating lamp can have the advantageous effects of preventing a material from penetrating from the glass body of the illuminating lamp whose substrate is similar to that of an SiO2 film. In addition, the illuminating lamp can impart an electromagnetic wave shielding function to the glass body of this illuminating lamp owing to the conductivity originated from the indium oxide and/or the tin oxide. In the case of ordinary erections, such as a building, external electromagnetic waves intrude thereinto through window glasses most frequently. It is extremely valuable to impart the electromagnetic shielding function to the window glass together with the self-cleaning function.